1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to an input-signal frequency error detection apparatus and a detection method thereof, and more particularly, to an input-signal frequency error detection apparatus and a detection method thereof calculating and analyzing histogram information on an input signal, and detecting frequency errors of the input signal.
2. Description of the Related Art
In general, when a signal reception system for communication equipment or data storage devices receives signals, the signal reception system detects a frequency of an RF signal transmitted from a signal transmission system, and synchronizes an operational frequency of the signal reception system with the frequency of the RF signal. A frequency synchronization circuit is needed for such frequency synchronization, and, in particular, for frequency synchronization circuits, a frequency detector is needed. In general, there exists an error between an operational frequency of a signal reception system and a frequency detected based on an RF signal inputted to a frequency detector, so a frequency error detection apparatus has been used to compensate for such an error.
FIG. 1 is a view for showing timings for detecting period information on periodic signals of an input signal, and FIG. 2 is a block diagram for showing a conventional frequency error detection apparatus.
FIG. 1 indicates an input signal at ‘a’, and, in particular, the solid line indicates an inputted analog signal and the dotted lines indicate converted digital values. FIG. 1 also indicates data clocks at ‘b’, a process counting data clock periods at ‘c’, count result values of the data clock periods for a periodic signal at ‘d’, which indicate an interval between zero crossing points and is referred to as period information in the present disclosure, and count values of zero crossing points at ‘e’.
Hereinafter, descriptions are made on a DVD system as an exemplary signal reception system to which a signal is inputted, for the convenience of explanations.
The conventional frequency error detection apparatus is provided in the DVD system, and includes an A/D converter 10, a zero crossing point detector 11, a period information detector 12, a zero crossing point counter/comparator 13, a maximum period detector 14, and a frequency error calculator 15.
The A/D converter 10 samples and converts an analog input signal into digital values for an output. For non-zero values, the digital values each have either a positive sign or a negative sign.
The zero crossing point detector 11 detects sign changes of the converted digital values so as to detect and output zero crossing points at which signal polarities are changed.
The period information detector 12 detects and outputs period information of a periodic signal based on the detected zero crossing points. Here, the period information as described above is referred to as the number of digital values corresponding to each periodic signal, or, in other words, referred to as the number of data clock periods corresponding to each periodic signal. In the embodiment shown in FIG. 1, a first periodic signal has period information of 5T, and a second periodic signal has period information of 2T.
The zero crossing point counter/comparator 13 counts the number of detected zero crossing points when the zero crossing points are detected. Further, the zero crossing point counter/comparator 13 decides whether the number of zero crossing points counted so far is equal to the number of error-detection-target, zero crossing points initially set. If equal, the zero crossing point counter/comparator 13 outputs a predetermined signal to the zero crossing point detector 11 in order for the zero crossing point detector 11 to stop detecting zero crossing points.
The maximum period detector 14 detects a periodic signal having maximum period information form detected period information. The DVD system has period information of 3T˜11T for a periodic signal corresponding to data information, and has period information of 14T for a synchronization signal necessary for frequency synchronization. Accordingly, in the DVD system, a periodic signal having the period information of 14T is a period signal having the maximum period information and, at the same time, corresponds to a synchronization signal, and the maximum period detector 14 detects and outputs signal having the period information of 14T to the frequency error calculator 15.
The frequency error calculator 15 stores a reference synchronization signal detected in the normal state of the DVD system. Further, the frequency error calculator 15 calculates a difference value between the stored reference synchronization signal and an inputted periodic signal having the maximum period information, and calculates a frequency error value (FE) through a predetermined process based on the calculated difference value. The frequency of an input signal inputted in the DVD system is synchronized with the operational frequency of the DVD system based on the calculated frequency error value.
However, the DVD system detects a synchronization signal having predetermined period information inserted in every certain interval, i.e., in every 1488 bits of data. For example, the DVD system detects a periodic signal having 14 clock period information. The synchronization with the operational frequency of the DVD system is achieved based on the detected synchronization signal. Accordingly, the existing frequency error detection apparatus has to detect at least one synchronization signal in order to achieve the frequency synchronization of the DVD system, and needs to search a large number of intervals, for example, at least 1488 data intervals in order to detect at least one synchronization signal.
However, since most of the systems have to accomplish frequency synchronization within a short time, the time required for searching a large number of intervals causes a problem in the operations of the DVD systems.
Further, when the polarity changes of an input signal as in FIG. 1 are merely used in order to detect the period information of a synchronization signal, the polarities of digital values near zero crossing points may be detected to be opposite of the original polarities under circumstances in which noise is externally added. Accordingly, there is a problem in that the accuracy of frequency error detection can be degraded.